The present disclosure relates to a sheet feeder used to stock a large number of sheets such as sheets of paper to be supplied to an apparatus, and relates also to an image forming apparatus incorporating such a sheet feeder.
Sheet feed cassettes are used in image forming apparatuses as exemplified by copier and printers for the purpose of feeding sheets of cut paper. A sheet feed cassette stocks a large number of unprinted sheets of paper and feeds them one by one separately from the topmost layer of the sheets stacked inside the cassette.
Some sheet feed cassettes are provided with a lift plate on the top face of which sheets are placed. The lift plate is, at its upstream-side end with respect to the sheet feed direction, supported on the inner bottom face of the cassette body, and is rotatable about this pivoted end, with a downstream-side end part of the lift plate with respect to the sheet feed direction acting as a rotatable end. The rotatable end of the lift plate is raised by a driving means, such as a lift motor provided in an image forming apparatus, and a biasing means, such as a spring. This permits the downstream-side end of the sheets placed on the lift plate to be moved to a proper sheet feed position, and thereby enables stable sheet feeding.
As described above, the lift plate is, at its upstream-side end with respect to the sheet feed direction, supported so as to be rotatable about this pivoted end, with the downstream-side end of the lift plate acting as a rotatable end. Thus, when the image forming apparatus is transported with the sheet feed cassette loaded in it, vibration or impact may cause the lift plate to rotate. This inconveniently leads to the lift plate colliding with a member nearby, causing damage to the lift plate itself or to the member nearby.
As a solution, a sheet feed cassette is known which is provided with an engaged portion provided on a lift plate, a locking member provided on a cassette body, a biasing means for biasing the locking member in a direction for engagement with the engaged portion, and a locking member controlling means for moving the locking member in an unlocking direction by moving the lift plate in a direction for a flat-lying direction and for permitting the biasing member to move the locking member in a direction for engagement with the engaged portion when the lift plate is in a flat-lying position.
Also known is a sheet feeding device which includes a lift plate fixing member. This member can be put through a lift hole formed through a lift plate and through a locking hole provided in an accommodating face opposite it, has at its lower end an engagement projection that engages with the reverse face of the accommodating face when the member is put through those holes, and has in an upper part thereof a pressing piece that locks the top face of the lift plate.
Further known is a sheet feed cassette wherein, by moving in the axial direction a lift plate swinging shaft provided with a lift plate raising plate, an engagement portion provided on the reverse face of a lift plate and the lift plate raising plate are engaged with each other and thereby the lift plate is locked so as not to swing.
Inconveniently, however, the configuration provided with an engaged portion, a locking member, and a locking member controlling means requires the separate provision of the locking member and a compression spring (biasing means) for biasing the locking member, and also requires a complicated construction where the lift plate needs to be provided with a locked portion (engaged portion) and the image forming apparatus body needs to be provided with an unlocking projection. Moreover, this technology is directed to a configuration where a lift plate is biased in a rising direction by an elastic basing member, and is difficult to apply to a configuration where a lift plate is raised and lowered by use of a lift motor and an actuating plate.
On the other hand, the configuration including a lift plate fixing member requires the fitting of the lift plate fixing member before transport and the removal of the lift plate fixing member before use, spoiling ease of handling. Moreover, failure to fit or remove the lift plate fixing member may lead to damage to the lift plate. Furthermore, the need for a dedicated fixing member results in higher cost. The method involving locking the lift plate so as not to swing by use of a lift plate swinging shaft requires the lift plate swinging shaft to be moved in the axial direction to lock or unlock the rotation of the lift plate, resulting in a complicated configuration.
Although the foregoing discusses sheet feed cassettes that stock sheets of paper as a recording medium to feed them to an image forming section, similar problems are encountered with automatic document feeders that stock a stack of sheets of a document to feed them one by one to an image reading portion so long as they are so configured as to raise and lower a lift plate by use of a lift motor and an actuating plate.